Highly selective electrochemical fluorination of organic compounds in ionic liquids

Recent studies on electrochemical partial fluorination in ionic liquid fluoride salts are reviewed. At first, historical background and some problems of electrochemical fluorination in organic solvents are briefly mentioned. Solvent-free electrochemical fluorinations in ionic liquids are explained as follows. Ultrasonication was found to improve both the yield and current efficiency for electrochemical fluorination of α-phenylthioacetate, which is mainly attributable to marked mass transport promotion of the substrate and the suppression of anode passivation. Highly regioselective and efficient fluorination of cyclic ethers, lactones, and cyclic carbonate was achieved in Et₄NF·4HF and Et₃N·5HF. Selective fluorination of hardly oxidizable phthalide was realized using a combination of imidazolium and fluoride ionic liquids. The unique effect of imidazolium ionic liquids on electrochemical fluorodesulfurization of 3-phenylthiophthalide was explained. Reuse of ionic liquids for electrochemical fluorination is also possible.     

The electrochemical properties of a platinum electrode in functionalized room temperature imidazolium ionic liquids

The electrochemical behavior of a platinum electrode in a set of 1-alkyl ether (and 1-alkyl)-3-methylimidazolium room-temperature ionic liquids (RTILs) 1–3 ([C_xO_yMim]⁺[Anion]⁻ or [C_xMim]⁺[Anion]⁻, where Mim = 3-methylimidazolium; C_xO_y = 1-alkyl ether; C₇O₃ = -(CH₂)₂O(CH₂)₂O(CH₂)₂OCH₃; C₃O₁ = -(CH₂)₂OCH₃; C_x = 1-alkyl; C₁₀ = C₁₀H₂₁; C₄ = C₄H₉; and ) was studied by cyclic voltammetry and electrical conductivity. This complementary set of imidazolium RTILs allowed us to explore the effect of the imidazolium cation and the counter-ion, both of which affected the electrochemical window of these RTILs. Various electrochemical events with low current values were observed, which diminished the electrochemical windows. Interestingly, RTILs 2b [1-(2-methoxyethyl)-3-methylimidazolium tetrafluoroborate] and 2d [1-butyl-3-methylimidazolium tetrafluoroborate] showed quasireversible charge transfer processes. The length of the functional group attached to the imidazolium cation was shown to be of great influence as larger electrochemical windows, as well as lower electrical conductivities, were obtained with the longer C₇O₃ and C₁₀ functional groups. The largest electrochemical window of 2.0 V was achieved with RTIL 2c, 1-decyl-3-methylimidazolium tetrafluoroborate. Dedicated to the memory of Prof. Francisco Nart.     

基于离子液体-石墨烯-二茂铁的高灵敏电化学免疫传感器检测CEA

研究了在PBS缓冲介质中,一种检测癌胚抗原的新型免标记免疫电化学传感器的制备,将石墨烯、二茂铁的高效催化及壳聚糖的优良生物相容性和成膜性、离子液体的导电性等优势充分结合构建了电化学免疫传感器。通过循环伏安法及交流阻抗对修饰的电极进行表征,在最优条件下,癌胚抗原的质量浓度在0.2～50.0 ng/mL的范围内与差分脉冲伏安法峰电流呈良好的线性关系,回归方程为Δi=0.38-1.31ρ,相关系数分别为0.9967,检测限为0.06 ng/mL,该传感器可用于人血清样品的测定。     

The influence of ionic liquids on the fabrication of nonenzymatic glucose electrochemical sensor

Gold nanoparticles (GNPs) embedded in a Bucky gel consisting of carbon nanotubes (CNTs) and ionic liquid (IL) show an excellent electrocatalytic activity to glucose oxidation owing to some synergistic effects among GNPs, CNTs and IL. Each component in such a composite has its specific function while there are complicate interactions among them. Based on this strategy, the use of composite as the modified coating allows the fabrication of a novel nonenzymatic glucose electrochemical sensor, which shows a substantial enhancement in detection sensitivity. This paper centers on the influence of several ILs with various anions and cations as well as alkyl branch lengths on the function of sensor. Based on our results, the performance of the sensor is strongly influenced by ILs. A few conclusions can be drawn. Firstly, an imidazolium cation facilitates both the stability of sensor and the efficiencies of GNPs and CNTs, while the alkyl branch lengths have few effects on the performance of sensor. Secondly, a hydrophilic anion is beneficial to the formation of environment where the direct oxidation of glucose takes place. Thirdly, other anions such as BF₄⁻ and PF₆⁻ do not matter for imidazolium-based IL. Fourthly, non-imidazolium-based IL militates against the dispersion of CNTs and GNPs in Bucky gel, reducing the detection sensitivity to glucose. Of the ILs studied, the best performance for glucose determination is obtained with an IL mainly benefitted by the combination of imidazole and sulfonate.     

Photo-degradation of imidazolium ionic liquids

Degradation of imidazolium ionic liquid, [bmim⁺][TFSA⁻] and iodide solution of [bmim⁺][TFSA⁻] by UV-laser irradiation has been studied through ground-state absorption and transient absorption spectroscopy. We found that excited state [bmim⁺]* undergoes degradation efficiently.     

离子液体在导电高分子中的应用

综述了离子液体作为介质，在导电高分子合成及其电化学性能测试，以及导电高分子电化学器件中（电化学电容、发光电化学池、驱动器、太阳能电池）的最新研究进展。在此基础上。展望了离子液体在导电高分子中的应用前景。     

Combined dealkoxycarbonylation and lactonisation of unsaturated malonates in ionic liquids

Heating unsaturated malonates with LiCl and water in [bmim][Br] or [bmim][BF₄]/[bmim][Br] produces unsaturated esters or lactones, respectively.     

Electrophilic catalysis in nucleophilic substitution reactions in ionic liquids

2-Chlorotropone was obtained from 2-tosyloxytropone in 88% yield in the recyclable ionic medium BMIMBF₄/LiCl. That Li⁺ acts as a Lewis acid was proven by the lack of reactivity of 2-tosyloxytropone, under the above conditions, on replacing LiCl with NaCl or BMIMCl, or using BMIMCl alone, or a BMIMBF₄/MeCN/KCl mixture. 2-Bromo- and 2-iodotropone were obtained along similar lines from LiBr or LiI, respectively, whereas LiF proved unreactive.     

Synthesis of fluoromethylated materials in ionic liquids

Syntheses of fluoromethylated materials via Michael additions with the Baylis-Hillman type reaction and the reaction of fluoromethylated imines with enamines in ionic liquid are described.     

Application of ionic liquids as low-volatility plasticizers for PMMA

Room temperature ionic liquids (ILs) based on imidazolium salts, were found to be excellent plasticizers for poly(methyl methacrylate), with improved thermal stability, and the ability to reduce glass transition temperatures to near 0 °C. Because ILs have environmentally benign properties, they can be used in place of traditional chemicals in numerous products and processes. In this work, PMMA was formulated using dioctyl phthalate, DOP, as a traditional plasticizer, and properties were compared to PMMA plasticized with two ILs: butyl methylimidazolium/hexafluorophosphate, [bmim⁺][PF₆⁻], and hexyl methylimidazolium/hexafluorophosphate, [hmim⁺][PF₆⁻]. Formulations incorporated up to 30 vol.% DOP and 50 vol.% ILs. Bulk and plasticized polymers were characterized for glass transition temperature, elastic modulus, and the thermal stability of the plasticizers.     

Electrochemical synthesis and characterization of poly(3,4-ethylenedioxythiophene) in ionic liquids with bulky organic anions

The electrochemistry of poly(3,4-ethylenedioxythiophene) (PEDOT) was studied in two ionic liquids with bulky organic anions, i.e., 1-butyl-3-methylimidazolium (BMIM) diethylene glycol monomethyl ether sulfate (MDEGSO₄) and BMIM octyl sulfate (OctSO₄). BMIM-MDEGSO₄ is a liquid, while BMIM-OctSO₄ is in solid form at room temperature. Electrosynthesis of PEDOT in BMIM-MDEGSO₄ with an EDOT concentration of 0.1 M and in BMIM-MDEGSO₄/EDOT 1/1 (w/w) solution resulted in no polymer at all or a very limited amount of polymer on the electrode surface, as determined by cyclic voltammetry in 0.1 M KCl(aq) solution. In contrast, electrosynthesis of PEDOT in BMIM-OctSO₄/EDOT 1/1 (w/w) resulted in a high yield of electroactive material on the electrode surface. Furthermore, electrosynthesis of PEDOT in ionic liquid–water solution (C_{ionic liquid}=1.5 M) containing 0.1 M EDOT was also found to give a relatively high yield of electroactive material on the electrode surface, both for 1.5 M BMIM-MDEGSO₄(aq) and 1.5 M BMIM-OctSO₄(aq). The PEDOT electrodes showed an anionic potentiometric response in 10^–5–10^–1 M KCl(aq) solution, indicating a predominant anion transfer at the polymer–solution interface despite the relatively bulky anions (MDEGSO₄^– or OctSO₄^–) incorporated as counterions in PEDOT during electropolymerization. On the basis of electrochemical impedance spectroscopy, the charge (ion) transport properties of the polymer film were strongly influenced by the water content of the ionic liquid (C_{ionic liquid}=0.05–2.0 M).Dedicated to Zbigniew Galus on the occasion of his 70th birthday     

Enzymatic polyester synthesis in ionic liquids

The enzymatic synthesis of polyesters by ring-opening polymerization (ROP) and polycondensation in three ionic liquids, i.e., [bmim][Tf₂N], [bmim][PF₆] and [bmim][BF₄] was investigated. For the enzymatic ROP of ε-caprolactone it was found that [bmim][PF₆] and [bmim][BF₄] result in an inhomogeneous reaction mixture upon polymerization, causing polymerization characteristics similar to bulk polymerization. In contrast, for [bmim][Tf₂N] characteristics similar to toluene were observed. Molecular weights of 7000-9500 g/mol were obtained. In the polycondensation of dimethyl adipate and dimethyl sebacate, respectively, with 1,4-butanol the low volatility of ionic liquids was successfully utilized to perform the reactions in an open vessel at temperatures close to the boiling point of the condensation by-product. Molecular weights up to 5400 g/mol were obtained. This, in combination with the tunable solvent hydrophilicity of ionic liquids could offer an advantage in the polymerization of highly polar monomers with low solubility in organic solvents.     

Catalytic asymmetric hydrogenation of aromatic ketones in room temperature ionic liquids

Polar bisphosphonic acid-derived Ru(BINAP)(DPEN)Cl₂ precatalysts were synthesized and immobilized in room temperature ionic liquids (RTILs) for asymmetric hydrogenation of aromatic ketones with ee values of up to 98.7%. The performance of the Ru catalysts is highly dependent on the nature of imidazolium ILs. For the imidazolium ILs without acidic protons, both ILs and Ru catalysts were recycled by simple extraction and reused. Such a simple immobilization approach also prevented the leaching of Ru (and Ru catalysts) into the chiral secondary alcohol products, and should prove desirable for the production of pharmaceutical intermediates that are free from metal contaminants.     

Enabling new electrochemical methods with redox-active ionic liquids

Redox-active ionic liquids are obtained by tethering an electroactive center to either the cation, the anion, or both ions in an ionic liquid. While such phases were studied back in the 1990s for their particular electrochemical behavior, they are currently under increased scrutiny for applications in electrochemical systems. This contribution identifies the redox-active ionic liquids’ most important aspects to promote their development. This article provides a review of their features and offers several design guidelines. In addition, it offers an overview of the key properties which enhance their suitability as electrolytes in electrochemical systems, with particular attention paid to lithium-ion batteries and electrochromic devices.     

Synthesis of bis-ANS fluorescence probe in ionic liquids

A new application of ionic liquids in the preparation of fluorescence probe 5,5'-bis-8-phenylamino-l-naphthylsulfonate (bis-ANS) is represented. The method for the preparation of fluorescence probe bis-ANS in alkyl imidazolinm cationic liquids under acidic conditions is described. The effects on reaction yields under different concentration of sodium nitrite and different ionic liquid were studied and good yields were achieved.     

Effect of ionic liquids in unimolecular solvolysis reactions involving carbocationic intermediates

Solvolysis studies of pivaloyl triflate were performed using ionic liquid/methanol solvent mixtures. The rearranged carbocation intermediate reacts with methanol via nucleophilic attack or elimination of a proton. Relative amounts of products were determined through ¹H NMR analysis. For most ionic liquids, increasing the ionic liquid:methanol ratio leads to increased yields of elimination product. Product ratios vary based on Kamlet–Taft solvatochromic parameters of hydrogen bond donating and accepting ability of the ionic liquid.     

A new fluorinated anion for room-temperature ionic liquids

A new room-temperature ionic liquid (RTIL) consisting of the fluorinated anion bis(trifluoromethyl)-phosphinate((CF₃)₂PO₂⁻) coupled with the 1-butyl-3-methyl-imidazoliuim (BMIM) cation has been synthesized and characterized by physicochemical and electrochemical means including differential scanning calorimetry (DSC), thermogravimetric analysis, viscosity, conductivity and cyclic voltammetry measurements. Properties are compared with those of the known RTIL consisting of BMIM coupled with the bis(trifluoromethyl)-sulfonylimide (TFSI) anion.     

Novel all-cellulose ecocomposites prepared in ionic liquids

In this study, a kind of novel all-cellulose ecocomposites based on cellulose and rice husk (RH) has been prepared by using green solvent, ionic liquid (IL), as processing medium. Due to the presence of the RH, these ecocomposites also contain an inorganic component, silica. The content and distribution of the silica in the ecocomposite have been investigated by energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) analyses. The mechanical properties of these ecocomposites, including both static and dynamic, have been determined by using tensile test and dynamic mechanical analysis (DMA), respectively. The effect of processing conditions on the interfacial bonding and therefore the mechanical performance of the final ecocomposites has been investigated further. Results show that the incorporation of the RH can provide stiffening effect for cellulose matrix, and the pretreatment of RH fillers by IL can enhance the filler/matrix interfacial bonding, thus further improving the mechanical performance of the ecocomposite. By selecting suitable composition ratios and processing conditions optimal mechanical performance with the balance among stiffness, strength and elongation at break can be obtained.     

Diels-Alder reactions in pyridinium based ionic liquids

Diels-Alder reactions have been investigated in pyridinium based ionic liquids. These solvents are found to be more effective compared to the organic solvent studied, in enhancing the reaction rate and product yields. Recycled ionic liquids also gave excellent results.     

Direct electrochemical reduction of hemin in imidazolium-based ionic liquids

The direct electrochemical reduction of hemin, protoporphyrin(IX) iron(III) chloride, ligated with strong or weak heterocyclic bases, was investigated in the ionic liquids (IL), 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([omim][PF₆]), using cyclic voltammetry and chronocoulometry. Hemin complexed with N-methylimidazole (NMI) or with pyridine had E_1/2 values slightly (4–59 mV) more positive in IL (without electrolyte) than in methanol (1.0 M electrolyte) using a gold electrode. NMI-ligated hemin had a lower E_1/2 than pyridine-ligated hemin in either IL, consistent with the stronger electron donor characteristic of NMI. [Bmim][PF₆] solutions consistently yielded E_1/2 values 30 mV more negative than [omim][PF₆] solutions. The diffusion coefficients D_o of hemin in the IL ranged between 1.50 and 2.80×10⁻⁷ cm² s⁻¹, while the heterogeneous electron-transfer rate constants k_s ranged between 3.7 and 14.3×10⁻³ cm s⁻¹. Cyclic voltammetry of hemin adsorbed to a gold surface through 4,4′-bispyridyl disulfide (AT4) linkages showed a large positive shift in the oxidation wave, indicating that adsorption stabilizes the reduced hemin state. The surface concentration Γ_o of the adsorbed hemin was determined to be 1.21×10⁻¹⁰ mol cm⁻², indicating the presence of one or more complete monolayers of hemin. These findings suggest that while hemin is electrochemically active in IL, its behavior is modified by the ligand field strength and surface adsorption phenomena.